Bifurcated stent delivery system having retractable sheath

ABSTRACT

An improved catheter assembly and method are provided for treating bifurcated vessels. The catheter assembly of the present invention includes a tubular sheath for restraining dual balloons normally biased apart. Withdrawal of the sheath allows the balloons to separate and deploy intravascular stents in a bifurcated vessel. The catheter assembly also includes the feature of containing two guide wire lumens in a single catheter designed to track over a single wire prior to arrival at the bifurcation, thus preventing wire wrapping and crossing of the wires.

This application is a division of U.S. Ser. No. 09/459,004 filed Dec.10, 1999 now U.S. Pat. No. 6,254,593.

BACKGROUND OF THE INVENTION

The invention relates to a stent delivery system for use at abifurcation and, more particularly, a bifurcated stent delivery systemhaving a retractable sheath.

Stents conventionally repair blood vessels that are diseased. Stents aregenerally hollow and cylindrical in shape and have terminal ends thatare generally perpendicular to their longitudinal axes. In use, theconventional stent is positioned at the diseased area of a vessel and,after placement, the stent provides an unobstructed pathway for bloodflow.

Repair of vessels that are diseased at a bifurcation is particularlychallenging since the stent must overlay the entire diseased area at thebifurcation, yet not itself compromise blood flow. Therefore, the stentmust, without compromising blood flow, overlay the entire circumferenceof the ostium to a diseased portion and extend to a point within andbeyond the diseased portion. Where the stent does not overlay the entirecircumference of the ostium to the diseased portion, the stent fails tocompletely repair the bifurcated vessel. Where the stent overlays theentire circumference of the ostium to the diseased portion, yet extendsinto the junction comprising the bifurcation, the diseased area isrepaired, but blood flow may be compromised in other portions of thebifurcation. Unopposed stent elements may promote lumen compromiseduring neointimalization and healing, producing restenosis and requiringfurther procedures. Moreover, by extending into the junction comprisingthe bifurcation, the stent may block access to portions of thebifurcated vessel that require performance of further interventionalprocedures. Similar problems are encountered when vessels are diseasedat their angled origin from the aorta as in the ostium of a rightcoronary or a vein graft. In this circumstance, a stent overlaying theentire circumference of the ostium extends back into the aorta, creatingproblems, including those for repeat catheter access to the vesselinvolved in further interventional procedures.

Conventional stents are designed to repair areas of blood vessels thatare removed from bifurcations and, since a conventional stent generallyterminates at right angles to its longitudinal axis, the use ofconventional stents in the region of a vessel bifurcation may result inblocking blood flow of a side branch or fail to repair the bifurcationto the fullest extent necessary. The conventional stent might be placedso that a portion of the stent extends into the pathway of blood flow toa side branch of the bifurcation or extend so far as to completely coverthe path of blood flow in a side branch. The conventional stent mightalternatively be placed proximal to, but not entirely overlaying, thecircumference of the ostium to the diseased portion. Such a position ofthe conventional stent results in a bifurcation that is not completelyrepaired. The only conceivable situation in which the conventionalstent, having right-angled terminal ends, could be placed where theentire circumference of the ostium is repaired without compromisingblood flow, is where the bifurcation is formed of right angles. In suchscenarios, extremely precise positioning of the conventional stent isrequired. This extremely precise positioning of the conventional stentmay result with the right-angled terminal ends of the conventional stentoverlaying the entire circumference of the ostium to the diseasedportion without extending into a side branch, thereby completelyrepairing the right-angled bifurcation.

To circumvent or overcome the problems and limitations associated withconventional stents in the context of repairing diseased bifurcatedvessels, a stent that consistently overlays the entire circumference ofthe ostium to a diseased portion, yet does not extend into the junctioncomprising the bifurcation, may be employed. Such a stent would have theadvantage of completely repairing the vessel at the bifurcation withoutobstructing blood flow in other portions of the bifurcation. Inaddition, such a stent would allow access to all portions of thebifurcated vessel should further interventional treatment be necessary.In a situation involving disease in the origin of an angulatedaorto-ostial vessel, such a stent would have the advantage of completelyrepairing the vessel origin without protruding into the aorta orcomplicating repeat access.

In addition to the problems encountered by using the prior art stents totreat bifurcations, the delivery platform for implanting such stents haspresented numerous problems. For example, a conventional stent isimplanted in the main vessel so that a portion of the stent is acrossthe side branch, so that stenting of the side branch must occur throughthe main-vessel stent struts. In this method, commonly referred to inthe art as the “monoclonal antibody” approach, the main-vessel stentstruts must be spread apart to form an opening to the side branch vesseland then a catheter with a stent is delivered through the opening. Thecell to be spread apart must be randomly and blindly selected byrecrossing the deployed stent with a wire. The drawback with thisapproach is there is no way to determine or guarantee that themain-vessel stent struts are properly oriented with respect to the sidebranch or that the appropriate cell has been selected by the wire fordilatation. The aperture created often does not provide a clear openingand creates a major distortion in the surrounding stent struts. There isno way to tell if the main-vessel stent struts have been properlyoriented and spread apart to provide a clear opening for stenting theside branch vessel.

In another prior art method for treating bifurcated vessels, commonlyreferred to as the “Culotte technique,” the side branch vessel is firststented so that the stent protrudes into the main vessel. A dilatationis then performed in the main vessel to open and stretch the stentstruts extending across the lumen from the side branch vessel.Thereafter, the main-vessel stent is implanted so that its proximal endoverlaps with the side branch vessel. One of the drawbacks of thisapproach is that the orientation of the stent elements protruding fromthe side branch vessel into the main vessel is completely random.Furthermore, the deployed stent must be recrossed with a wire blindlyand arbitrarily selecting a particular stent cell. When dilating themain vessel stretching the stent struts is therefore random, leaving thepossibility of restricted access, incomplete lumen dilatation, and majorstent distortion.

In another prior art device and method of implanting stents, a “T” stentprocedure includes implanting a stent in the side branch ostium of thebifurcation followed by stenting the main vessel across the side branchostium. In another prior art procedure, known as “kissing” stents, astent is implanted in the main vessel with a side branch stent partiallyextending into the main vessel creating a double-barreled lumen of thetwo stents in the main vessel proximal to the bifurcation. Another priorart approach includes a so-called “trouser legs and seat” approach,which includes implanting three stents, one stent in the side branchvessel, a second stent in a distal portion of the main vessel, and athird stent, or a proximal stent, in the main vessel just proximal tothe bifurcation.

All of the foregoing stent deployment assemblies suffer from the sameproblems and limitations. Typically, there are uncovered intimal surfacesegments on the main vessel and side branch vessels between the stentedsegments. An uncovered flap or fold in the intima or plaque will invitea “snowplow” effect, representing a substantial risk for subacutethrombosis, and the increased risk of the development of restenosis.Further, where portions of the stent are left unopposed within thelumen, the risk for subacute thrombosis or the development of restenosisagain is increased. The prior art stents and delivery assemblies fortreating bifurcations are difficult to use, making successful placementnearly impossible. Further, even where placement has been successful,the side branch vessel can be “jailed” or covered so that there isimpaired access to the stented area for subsequent intervention.

Attempts to bring any device, such as a bifurcated stent on a bifurcatedballoon assembly, to a bifurcation over two wires are prone to theproblem of wire wrapping. This phenomenon involves one wire crossing theother first anteriorly then posteriorly. The resulting wrapping thencreates resistance to advancement of the device, thus resulting infailure of deployment. Therefore, when delivering a device ultimatelyutilizing two wires, it would be desirable to first track the device inover a single wire, thus avoiding wire wrapping. The present inventionoffers a solution to these problems and others.

As used herein, the terms “proximal,” “proximally,” and “proximaldirection” when used with respect to the invention are intended to meanmoving away from or out of the patient, and the terms “distal,”“distally,” and “distal direction” when used with respect to theinvention are intended to mean moving toward or into the patient. Thesedefinitions will apply with reference to apparatus, such as catheters,guide wires, stents, the like. When used with reference to body lumens,such as blood vessels and the like, the terms “proximal,” “proximally,”and “proximal direction” are intended to mean toward the heart; and theterms “distal,” “distally,” and “distal direction” are intended to meanaway from the heart, and particularly with respect to a bifurcated bloodvessel, are intended to mean in the direction in which the branchingoccurs.

SUMMARY OF THE INVENTION

The invention provides for a bifurcated stent delivery system having aretractable sheath. The system is designed for repairing a main vesseland a side branch vessel forming a bifurcation, without compromisingblood flow in other portions of the bifurcation, thereby allowing accessto all portions of the bifurcated vessel should further interventionaltreatment be necessary. The catheter and the retractable sheath aredesigned to reduce the likelihood of wire wrapping during the stentingprocedure.

In one aspect of the invention, there is provided a stent deliveryassembly for treating bifurcated vessels including a dual balloonY-shaped catheter. The catheter includes a first expandable member and asecond expandable member. A first guide wire lumen is provided forreceiving a first guide wire. The first guide wire lumen extends throughat least a portion of the catheter including the first expandablemember. A second guide wire lumen is provided for receiving a secondguide wire, the second guide wire lumen extends through at least aportion of the catheter including the second expandable member. Atubular member is provided, wherein the first expandable member and thesecond expandable member are normally biased apart, but are restrainedand held together by the tubular member to provide a low profile duringdelivery of a Y-shaped stent.

In another aspect of the invention, a method is provided of stenting abifurcated vessel having a bifurcation, a first vessel branch, and asecond vessel branch. The method includes the step of providing a dualballoon Y-shaped catheter having a first expandable member and a secondexpandable member. A Y-shaped stent is mounted on the first and secondexpandable members. A tubular member is placed about the first andsecond expandable members such that the first and second expandablemembers are normally biased apart, but are restrained and held togetherby the tubular member. The Y-shaped stent is then delivered to a targetarea. The tubular member is withdrawn proximally until the firstexpandable member and the second expandable member are released andspring apart. The Y-shaped stent is next implanted by inflating thefirst and second expandable members. The first and second expandablemembers are then deflated and the catheter is withdrawn.

In yet another aspect of the invention, a method is provided of stentinga bifurcated vessel having a bifurcation, a first vessel branch, and asecond vessel branch. The method includes the step of providing a dualballoon Y-shaped catheter including a first expandable member and asecond expandable member. A first guide wire lumen is provided forreceiving a first guide wire. The first guide wire lumen extends throughat least a portion of the catheter including the first expandablemember. A second guide wire lumen is provided for receiving a secondguide wire. The second guide wire lumen extends through at least aportion of the catheter including the second expandable member. AY-shaped stent is mounted on the first and second expandable members. Atubular member is placed about the first and second expandable memberssuch that the first and second expandable members are normally biasedapart, but are restrained and held together by the tubular member. Asecond guide wire is positioned distally of the bifurcation in the firstvessel branch. The second guide wire is then backloaded into the secondguide wire lumen. Next, the catheter and tubular member are advancedover the second guide wire so that the catheter is advanced distally ofthe bifurcation in the first vessel branch. Alternatively, the cathetercan be advanced proximally of the bifurcation in the first vesselbranch. The tubular member is withdrawn proximally until the firstexpandable member and the second expandable member are released andspring apart. Next, the catheter is withdrawn proximally to a positionproximal of the bifurcation. A first guide wire is provided and advancedout of the first guide wire lumen and into the second vessel branchdistally of the bifurcation. The catheter is advanced distally over thefirst and second guide wires until the Y-shaped stent is positioned atthe bifurcation. The Y-shaped stent is then implanted by inflating thefirst and second expandable members. The first and second expandablemembers are deflated and the catheter and guide wires are withdrawn.

Other features and advantages of the present invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, which illustrate, by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of a bifurcation in which a prior art “T”stent is in a side branch ostium followed by the stenting of the mainvessel across the branch ostium.

FIG. 2 is an elevational view of a bifurcation in which “touching” priorart stents are depicted in which one stent is implanted in the sidebranch, a second stent implanted in a distal portion of the main vesselnext to the branch stent, with interrupted placement of a third stentimplanted more proximally in the main vessel.

FIG. 3 is an elevational view of a bifurcation depicting “kissing”stents where a portion of one stent is implanted in both the side branchand the main vessel and adjacent to a second stent implanted in the mainvessel creating a double-barreled lumen in the main vessel proximal tothe bifurcation.

FIG. 4 is an elevational view of a prior art “trouser legs and seat”stenting approach depicting one stent implanted in the side branchvessel, a second stent implanted in a proximal portion of the mainvessel, and a close deployment of a third stent distal to thebifurcation leaving a small gap between the three stents of an uncoveredlumenal area.

FIG. 5A is an elevational view of a bifurcation in which a prior artstent is implanted in the side branch vessel.

FIG. 5B is an elevational view of a bifurcation in which a prior artstent is implanted in the side branch vessel, with the proximal end ofthe stent extending into the main vessel.

FIG. 6 is an elevational view, partially in section, depicting anembodiment in which a Y-shaped catheter assembly deploys a Y-shapedstent in a bifurcation.

FIG. 7 is an elevational view depicting the Y-shaped catheter assemblyof FIG. 6 in which the stent is mounted on the expandable members of thecatheter.

FIG. 8 is a perspective view of the assembly of FIG. 7 shown partiallyinserted into the sheath.

FIG. 9 is an elevational view, partially in section, of a bifurcation inwhich the catheter of FIG. 7 is delivering the stent in the bifurcatedarea with the catheter inserted into the sheath.

FIG. 10 is an elevational view, partially in section, of a bifurcationin which the catheter of FIG. 7 is delivering the stent in thebifurcated area with the sheath being withdrawn proximally.

FIG. 11 is an elevational view, partially in section, of a bifurcationin which the catheter of FIG. 7 has been withdrawn proximally of thebifurcation and a guide wire is being extended into the second vesselbranch.

FIG. 12 is an elevational view, partially in section, of a bifurcationin which the catheter of FIG. 7 is implanted at the bifurcation.

FIG. 13 is another embodiment of the dual balloon Y-shaped catheter.

FIG. 14 is an elevational view, partially in section, of the dualballoon Y-shaped catheter of FIG. 13 restrained by the sheath.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the exemplary drawings wherein like reference numeralsindicate like or corresponding elements among the figures, the presentinvention includes a bifurcated stent delivery system for treatingbifurcated vessels in, for example, the coronary arteries, veins,arteries, and other vessels in the body.

Prior art attempts at implanting intravascular stents in a bifurcationhave proved less than satisfactory. For example, FIGS. 1-4 depict priorart devices which include multiple stents being implanted in both themain vessel and a side branch vessel. In FIG. 1, a prior art “T” stentis implanted such that a first stent is implanted in the side branchnear the ostium of the bifurcation, and a second stent is implanted inthe main vessel, across the side branch ostium. With this approach,portions of the side branch vessel are left uncovered, and blood flow tothe side branch vessel must necessarily pass through the main vesselstent, causing possible obstructions or thrombosis.

Referring to FIG. 2, three prior art stents are required to stent thebifurcation. In FIG. 3, the prior art method includes implanting twostents side by side, such that one tent extends into the side branchvessel and the main vessel, and the second stent is implanted in themain vessel. This results in a double-barreled lumen which can presentproblems such as thrombosis, and turbulence in blood flow. Referring tothe FIG. 4 prior art device, a first stent is implanted in the sidebranch vessel, a second stent is implanted in a proximal portion of themain vessel, and a third stent is implanted distal to the bifurcation,thereby leaving a small gap between the stents and an uncovered lumenalarea.

Referring to FIGS. 5A and 5B, a prior art stent is configured fordeployment in side branch vessel 5. In treating side branch vessel 5, ifa prior art stent is used, a condition as depicted will occur. That is,a stent deployed in side branch vessel 5 will leave a portion of theside branch vessel exposed, or as depicted in 5B, a portion of the stentwill extend into main vessel 6.

Turning to FIGS. 6-12, in one embodiment of the present invention, stentdelivery assembly 10 is provided for treating bifurcated vessels. Inthis embodiment, a Y-shaped stent is implanted to cover the bifurcation.Catheter 12 can be configured as a dual balloon Y-shaped catheter havinga proximal end and a distal end. The catheter includes first expandablemember 14 and second expandable member 16 that are configured to resideside-by-side (Y-shaped) for low profile delivery and to spring apart forimplanting Y-shaped stent 18. Each of the expandable members has aproximal end and a distal end. The stent is removably mounted on thefirst and second expandable members.

A first guide wire lumen 20 is provided for receiving first guide wire22. The first guide wire lumen extends through at least a portion ofcatheter 12 including first expandable member 14. A second guide wirelumen 24 is provided for receiving second guide wire 26. The secondguide wire lumen extends through at least a portion of the catheterincluding second expandable member 16. The expandable members can beinflatable non-distensible balloons. The guide wires 22, 26 preferablyare stiff wires each having a diameter of 0.014 inch, but can havedifferent diameters and degrees of stiffness as required for aparticular application. A particularly suitable guide wire can includethose manufactured and sold under the tradenames Sport® and Ironman®,manufactured by Advanced Cardiovascular Systems, Incorporated, SantaClara, Calif.

A tubular member, such as sheath 28, is provided, wherein the firstexpandable member and the second expandable member are normally biasedapart, but are restrained and held together by the sheath to provide alow profile during delivery of Y-shaped stent 18. The sheath can beformed from a polymer such as polyethylene, polyurethane, and nylons,although other similar polymeric material may also be suitable, such aspolyetheretherketone (PEEK), polytetrafluoroethylene (PTFE),polyethylene terephthalate (PET), and the like. Other suitable materialscan be used as are known to those skilled in the art.

The catheter 12 further includes an inflation lumen (not shown) forinflating first and second expandable members 14, 16 simultaneously. Theexpandable members can be inflated by delivering a suitable inflationmedia, such as saline, to the expandable members via the inflationlumen. In one embodiment, the second expandable member is longer thanthe first expandable member so that distal portion 30 of the secondexpandable member protrudes from sheath 28 during delivery to facilitatetracking.

In one method of stenting a bifurcated vessel, as shown in FIGS. 9-12,Y-shaped stent 18 is mounted on first and second expandable members 14,16. The second guide wire 26 is positioned distal of the bifurcation infirst vessel branch 6. The second guide wire is then back loaded intosecond guide wire lumen 24. The catheter 12 and sheath 28 are advancedover the second guide wire so that the catheter is advanced distally ofthe bifurcation in the first vessel branch. During the advancement ofthe catheter, the first and second expandable members are restrained andheld together by sheath. Consequently, the sheath helps to provide a lowprofile during delivery of the stent.

In keeping with the invention, sheath 28 is withdrawn proximally untilfirst expandable member 14 and second expandable member 16 are releasedand spring apart. The catheter 12 is then withdrawn proximally to aposition proximal of the bifurcation. In one embodiment, first guidewire 22 has been contained as an integrated guide wire within firstguide wire lumen 20 up to this point. Alternatively, the first guidewire may be inserted into the proximal end of the first guide wire lumenat this time. The first guide wire is then advanced out of the firstguide wire lumen and into second vessel branch 5 distally of thebifurcation.

If, after withdrawal of the sheath to release the expandable members,the device is seen to be oriented such that first expandable member 14is further away from vessel 5 than is second expandable member 16, itmay be desirable to withdraw second guide wire 26 and readvance it intovessel 5 with first guide wire 22 then advanced into vessel 6. Thisreassignment of wires permits avoidance of rotation of more than 90degrees. In situations in which there is concern about recrossing of thelumen of the side branch vessel with either wire, this wire reassignmentis performed before catheter 12 is withdrawn proximal to thebifurcation.

The Y-shaped stent 18 is implanted by advancing distally over first andsecond guide wires 22, 26 until the stent is positioned at thebifurcation in apposition with carina 32. Due to the appropriate wireselection, rotation of no more than 90 degrees will be required. Thestent is implanted by inflating first and second expandable members 14,16, which are designed to inflate simultaneously. Then the first andsecond expandable members are deflated and the catheter and guide wirescan be withdrawn from the patient's vasculature. The novel arrangementof sheath 28 and guide wires 22, 26 and their respective lumens permitsingle unit transport of a Y-shaped stent to the distal target sitewithout wire wrapping problems and it allows for minimal requirements ofrotation of the device (less than 90 degrees) for optimal deployment(allowing minimal twist deformity).

In a related method, Y-shaped stent 18 is mounted on first and secondexpandable members 14, 16. The second guide wire 26 is positioned distalof the bifurcation in first vessel branch 6. The second guide wire isthen back loaded into second guide wire lumen 24. The catheter 12 andsheath 28 are advanced over the second guide wire so that the catheteris advanced proximally of the bifurcation in the first vessel branch.During the advancement of the catheter, the first and second expandablemembers are restrained and held together by the sheath. Consequently,the sheath helps to provide a low profile during delivery of the stent.

In keeping with the invention, sheath 28 is withdrawn proximally untilfirst expandable member 14 and second expandable member 16 are releasedand spring apart. In one embodiment, first guide wire 22 has beencontained as an integrated guide wire within first guide wire lumen 20up to this point. Alternatively, the first guide wire may be insertedinto the proximal end of the first guide wire lumen at this time. Thefirst guide wire is then advanced out of the first guide wire lumen andinto second vessel branch 5 distally of the bifurcation.

Next, catheter is advanced distally over first and second guide wires22, 26 until Y-shaped stent 18 is positioned at the bifurcation inapposition with carina 32. Due to the appropriate wire selection,rotation of no more than 90 degrees will be required. The stent isimplanted by inflating first and second expandable members 14, 16, whichare designed to inflate simultaneously. Then the first and secondexpandable members are deflated and the catheter and guide wires can bewithdrawn from the patient's vasculature. The novel arrangement ofsheath 28 and guide wires 22, 26 and their respective lumens permitsingle unit transport of a Y-shaped stent to the distal target sitewithout wire wrapping problems and it allows for minimal requirements ofrotation of the device (less than 90 degrees) for optimal deployment(allowing minimal twist deformity).

Notably, it is contemplated that the methods of the present inventioncan be accomplished with any suitable catheter 12. Referring to FIGS. 13and 14, another embodiment of the dual balloon Y-shaped catheter isdepicted. The catheter has first stem 40 and second stem 42. The firststem 40 is connected to first expandable member 14. The second stem 42is connected to second expandable member 16 having distal portion 30 fortracking. In this embodiment, the second expandable member isapproximately twice as long as the first expandable member; however, itis contemplated that the expandable members can be of varying lengths.The expandable members can be simultaneously inflated via an inflationlumen (not shown). The first guide wire 22 is positioned within thefirst expandable member and the second guide wire is positioned withinthe second expandable member. The first and second expandable membersare normally biased apart, but are restrained and held together bysheath 28 to provide a low profile during delivery of Y-shaped stent 18.

While the invention herein has been illustrated and described in termsof a catheter assembly and method of use, it will be apparent to thoseskilled in the art that the invention can be used in other instances.Other modifications and improvements may be made without departing fromthe scope of the invention.

What is claimed is:
 1. A method of stenting a bifurcated vessel having abifurcation, a first vessel branch, and a second vessel branch,comprising the steps of: providing a dual balloon Y-shaped catheterhaving a first expandable member and a second expandable member;providing a Y-shaped stent mounted on the first and second expandablemembers; providing a tubular member and placing it about the first andsecond expandable members such that the first and second expandablemembers are normally biased apart, but are restrained and held togetherby the tubular member; delivering the Y-shaped stent to a target area;withdrawing the tubular member proximally until the first expandablemember and the second expandable member are released and spring apart;implanting the Y-shaped stent by inflating the first and secondexpandable members; deflating the first and second expandable members;and withdrawing the catheter.
 2. The method of claim 1, wherein thetubular member is a sheath.
 3. A method of stenting a bifurcated vesselhaving a bifurcation, a first vessel branch, and a second vessel branch,comprising the steps of: providing a dual balloon Y-shaped catheterhaving a proximal end and a distal end, the catheter including a firstexpandable member having a proximal end and a distal end, the catheterfurther including a second expandable member having a proximal end and adistal end; providing a first guide wire lumen for receiving a firstguide wire, the first guide wire lumen extending through at least aportion of the catheter including the first expandable member; providinga second guide wire lumen for receiving a second guide wire, the secondguide wire lumen extending through at least a portion of the catheterincluding the second expandable member; providing a Y-shaped stentmounted on the first and second expandable members; providing a tubularmember and placing it about the first and second expandable members suchthat the first and second expandable members are normally biased apart,but are restrained and held together by the tubular member; providing asecond guide wire and positioning the second guide wire distally of thebifurcation in the first vessel branch; loading the second guide wireinto the second guide wire lumen; advancing the catheter and tubularmember over the second guide wire so that the catheter is advanceddistally of the bifurcation in the first vessel branch; withdrawing thetubular member proximally until the first expandable member and thesecond expandable member are released and spring apart; withdrawing thecatheter proximally to a position proximal of the bifurcation; providinga first guide wire; advancing the first guide wire out of the firstguide wire lumen and into the second vessel branch distally of thebifurcation; advancing the catheter distally over the first and secondguide wires until the Y-shaped stent is positioned at the bifurcation;implanting the Y-shaped stent by inflating the first and secondexpandable members; deflating the first and second expandable members;and withdrawing the catheter.
 4. The method of claim 3, wherein thetubular member is a sheath.
 5. A method of stenting a bifurcated vesselhaving a bifurcation, a first vessel branch, and a second vessel branch,comprising the steps of: providing a dual balloon Y-shaped catheterhaving a proximal end and a distal end, the catheter including a firstexpandable member having a proximal end and a distal end, the catheterfurther including a second expandable member having a proximal end and adistal end; providing a first guide wire lumen for receiving a firstguide wire, the first guide wire lumen extending through at least aportion of the catheter including the first expandable member; providinga second guide wire lumen for receiving a second guide wire, the secondguide wire lumen extending through at least a portion of the catheterincluding the second expandable member; providing a Y-shaped stentmounted on the first and second expandable members; providing a tubularmember and placing it about the first and second expandable members suchthat the first and second expandable members are normally biased apart,but are restrained and held together by the tubular member; providing asecond guide wire and positioning the second guide wire distally of thebifurcation in the first vessel branch; loading the second guide wireinto the second guide wire lumen; advancing the catheter and tubularmember over the second guide wire so that the catheter is advancedproximally of the bifurcation in the first vessel branch; withdrawingthe tubular member proximally until the first expandable member and thesecond expandable member are released and spring apart; providing afirst guide wire; advancing the first guide wire out of the first guidewire lumen and into the second vessel branch distal of the bifurcation;advancing the catheter distally over the first and second guide wiresuntil the Y-shaped stent is positioned at the bifurcation; implantingthe Y-shaped stent by inflating the first and second expandable members;deflating the first and second expandable members; and withdrawing thecatheter.
 6. The method of claim 5, wherein the tubular member is asheath.